I've been on the Internet when flamewars were common, and CoC weren't a thing yet.

CoC (along with committees) are a very recent thing. They weren't introduced until certain people started exercising moral blackmail onto projects, people and organizations by pushing political topics into technical discussions.

Back in the days of flamewars there were a few rules and pretty much just moderators to enforce them.

Rules were simple, you were usually banned if your messages were either not civil (and here again, the bar was high), if your contributions were comically off-topic or if you spammed the forum/newsgroup/mailing list.